For a long time past, adjusting devices of the general type described have been used in magnetic gradient probes for aligning the two probe elements of a gradient probe into exact parallelism relative to one another or relative to an assumed probe axis. Particularly in cases where gradient probes are part of a magnetic field detector, high precision and constancy are required for the adjusting devices. If, for example, the required resolution is to be in the order of 1.gamma. (1.gamma. = 10.sup.-5 Oersted), the parallelism must be adjusted with a precision of some seconds of arc, otherwise an indication error corresponding to the required resolution is to be expected on rotation of the probe in the geomagnetic field. An additional impediment exists in that no ferromagnetic materials may be used for the construction of such adjusting devices.
In the previously known adjusting devices, one end of the probe body was connected with one of the supporting bodies by means of a ball-and-socket joint. The second supporting body was provided with a threaded spindle extending in the transverse direction to the probe axis, the thread of which was engaged by a threaded sector secured to the other end of the probe body. To maintain the engagement in any adjusting position, the threaded sector had to be resiliently pressed onto the threaded spindle. For this purpose, it was necessary to support the component carrying the ball socket of the ball-and-socket joint so that it could be moved in the axial direction and to preload it by spring so that the spring force was transmitted to the threaded spindle through the ball-and-socket joint, the probe body and the threaded sector. Furthermore, a radial thrust bearing was required at the end of the probe body facing the threaded spindle to prevent movement of the probe body in a direction other than the desired adjusting direction.
A weighty disadvantage of this known form of adjusting device is, despite its relatively high cost, an improvement of the precision beyond a certain degree cannot be achieved. In particular, slight movements of the probe body cannot be completely avoided when adjusting the spindle. These movements are due to the fact that frictional forces are counteracting the adjustment of the probe body in the desired direction and that the probe core turns aside in the axial direction along the flanks of the threads. At this time the spring force in the axial direction increases. As soon as the spring force has attained the intensity of the frictional forces, the probe body suddenly slides back. To remedy this deficiency, the spring force and the frictional forces must be balanced with one another for each point of the adjusting range. The axial support of the part carrying the ball socket as well as the thrust bearing at the opposite end of the probe body must be manufactured with extremely close tolerances, since even the smallest play offers the possibility of parallelism deviation. The ball head and the ball socket must also be individually manufactured with high precision. Furthermore, in the previous construction, the diameter of the threaded spindle cannot be reduced below a certain degree as would be desirable for the improvement of the smooth running characteristics (fine-pitch).